The invention relates to a pipetting system with a pipetting device and at least one pipette tip releasably fastened thereto.
Such pipetting systems are above all used in the laboratory for metering fluid quantities. These fluids are suctioned into pipette tips and ejected therefrom. For this mostly pistons are displacably arranged in a cylinder. With air cushion systems the piston and cylinder are integrated into the pipetting device and communicate with the pipette tip so that the metering of the fluid is evaluated via an air cushion. With direct displacement systems the piston and the cylinder are integrated into the tip and act directly on the suctioned-in fluid. Such pipetting systems are also called syringes. Pistonless systems may in particular comprise a pipette tip with a balloon-like end section which expands for suctioning in fluid, and for expulsion is compressed.
The pipette tip is detachably connected to the pipetting device so that after usage it may be exchanged for a fresh pipette tip, by which means with subsequent meterings contaminations may be avoided. Pipette tips for one-off use are available inexpensively of plastic.
The pipetting devices have a fastening attachment for fastening pipette tips. Mostly this is a conical projection onto which is squeezed the pipette tip with a conical receiver. This may be effected without gripping the pipette tip by sticking the fastening attachment onto a pipette tip which is ready and waiting in a holder.
For avoiding contamination of the operating personnel it is furthermore desirable to release the pipette tip from the fastening attachment without grasping it. For this many pipetting devices are equipped with an ejection means which with an ejection sleeve is allocated to the upper edge region of the pipette tip and may be actuated on an ejection knob. With pipette tips which are stuck on particularly strongly or even "rammed on", for the ejection of the tips however a high force effort is required which already with one-channel systems compromises the use or even makes it impossible. A particularly high force effort may result by way of the multiplied tip ejection forces with multi-channel pipetting systems which have several parallel pipette tips to be ejected.
From EP 0 566 039 B1 there is known a pipette with a tip remover which for simplifying the use by way of reduction of the ejection force comprises a lever mechanism. This lever mechanism projects laterally from a pipette housing and is to be pressed manually. It may have a toothed wheel which on an actuation arm for the pipette tip is rotatably coupled in a vertical plane. Further the inner flank of the toothed wheel meshes with a rack on the side of the elongate housing. On the outer side of the actuation arm on the side of the housing there is arranged a hollow push-rod which with a thread on its inner side meshes with the outer side of the gearwheel. If the push-rod is pressed down, the toothed wheel moves downwards and simultaneously takes with it the actuation arm and an ejection sleeve, by which means a pipette tip is pushed back from a fastening cone. With this the push-rod covers exactly double the distance as the actuation arm and the force exerted on the push-rod is half as large as the force used for pushing back the pipette tip. This system is expensive in its design and permits only a single transmission ratio of 1:2 so that it is limited in its usability.